Under certain conditions of hypo- and hyperbaric decompression, gas supersaturation of tissues and blood can cause bubbles to form, with serious medical consequences. The early etiology of decompression sickness has received relatively little attention in the past and is poorly understood. For example, the biophysical basis for the very high in vivo susceptibility to bubble formation has not been established, and essential information is lacking as to where the bubbles form. Our objective is to increase the understanding of the phenomena that lead to decompression sickness. This will be accomplished by studies of bubble formation in gas supersaturated water, solutions, and suspensions of solids as well as in single cells and animals of varying morphological complexity; such organisms as invertebrates, fish and amphibians in various stages of development, ciliates, blood cells and macrophages will be used. Once the necessary basic information has been obtained, higher organisms will be examined. The specific aims for the next phase are: 1) to identify organisms which are susceptible to bubble formation at very low gas supersaturations, and to establish where the bubbles are initiated and if they form spontaneously or from gaseous nuclei; 2) to examine how the bubble-promoting properties of some surfaces are affected by biological fluids and surfactants; and 3) to determine if limited water availability may be a contributing factor to the high intracellular gas supersaturation tolerances. The experimental methods to be used include direct microscopic observations and high speed cinephotomicrographic recordings of events during decompressions from various hyberbaric to baric or hypobaric pressures, and assessment of post-decompression damage to cells and animals. The results will be used to formulate new concepts and approaches and to re-evaluate existing concepts relating to formation of bubbles in vivo. An increased understanding of the etiological events will aid in developing measures for the prevention and treatment of decompression sickness.